Actuator units with piezoelectric actuator elements are used, for example, for injecting fuel into combustion chambers of internal combustion engines. The piezoelectric actuator elements preferably consist of ceramic and are disposed in an actuator housing consisting, for example, of invar. As the different materials of the actuator housing and piezoelectric actuator element have different values for the respective coefficient of thermal expansion, different length changes of the piezoelectric actuator element and actuator housing may occur in the event of a change in the temperature acting on the actuator unit. This may shift the position of the piezoelectric actuator element with respect to a final control element so that the operative connection between the piezoelectric actuator element and the final control element is affected accordingly.
Patent specification DE 199 09 106 C2 discloses an actuator unit in which length changes resulting from different coefficients of thermal expansion for the different materials of actuator housing and piezoelectric actuator element can be equalized by the actuator housing being composed of an inner, middle and outer sleeve, at least two sleeves having a different coefficient of thermal expansion. The materials of the sleeves are selected such that, as a result of the different coefficients of thermal expansion of the individual sleeves, the different length changes in the actuator housing and piezoelectric actuator element are equalized.